Your video card is a 128 mb card. Not supported as there are just to many things to render. your video card is most likely has aided memory from your ram, which from the looks of it you have a laptop? So its ram is probably very low aswell. I'm surprised you get 21 fps at any time.

you will need a 512mb video card to play the game properly. What is your cpu, ram and OS?
I recommend to play the game having a 512mb video card, quad core cpu, 4 gbs of ram and windows 7.